The present invention relates generally to auditory prostheses and more particularly to auditory prostheses which are adjustable by a programming system.
Auditory prostheses have been utilized to modify the auditory characteristics of sound received by a user of that auditory prosthesis. Usually the intent of the prosthesis is, at least partially, to compensate for a hearing impairment of the user or wearer. Hearing aids which provide an acoustic signal in the audible range to a wearer have been well known and are an example of an auditory prosthesis. More recently, cochlear implants which stimulate the auditory nerve with an electrical stimulus signal have been used to improve the hearing of a wearer. Other examples of auditory prostheses are implanted hearing aids which stimulate the auditory response of the wearer by a mechanical stimulation of the middle ear and prostheses which otherwise electromechanically stimulate the user.
Hearing impairments are quite variable from one individual to another individual. An auditory prosthesis which compensates for the hearing impairment of one individual may not be beneficial or may be disruptive to another individual. Thus, auditory prostheses must be adjustable to serve the needs of an individual user or patient.
The process by which an individual auditory prosthesis is adjusted to be of optimum benefit to the user or patient is typically called "fitting". Stated another way, the auditory prosthesis must be "fit" to the individual user of that auditory prosthesis in order to provide a maximum benefit to that user, or patient. The "fitting" of the auditory prosthesis provides the auditory prosthesis with the appropriate auditory characteristics to be of benefit to the user.
This fitting process involves measuring the auditory characteristics of the individual's hearing, calculating the nature of the acoustic characteristics, e.g., acoustic amplification in specified frequency bands, needed to compensate for the particular auditory deficiency measured, adjusting the auditory characteristics of the auditory prosthesis to enable the prosthesis to deliver the appropriate acoustic characteristic, e.g., acoustic amplification in specified frequency bands, and verifying that this particular auditory characteristic does compensate for the hearing deficiency found by operating the auditory prosthesis in conjunction with the individual. In practice with conventional hearing aids, the adjustment of the auditory characteristics is accomplished by selection of components during the manufacturing process, so called "custom" hearing aids, or by adjusting potentiometers available to the fitter, typically an audiologist, hearing aid dispenser, otologist, otolaryngologist or other doctor or medical specialist.
Some hearing aids are programmable in addition to being adjustable. Programmable hearing aids store adjustment parameters in a memory which the hearing aid can utilize to provide a particular auditory characteristic. Typically the memory will be an electronic memory, such as a register or randomly addressable memory, but may also be other types of memories such as programmed cards, switch settings or other alterable mechanisms having retention capability. An example of a programmable hearing aid which utilizes an electronic memory, in fact a plurality of memories, is described in U.S. Pat. No. 4,425,481, Mangold et al. With a programmable hearing aid which utilizes electronic memory, a new auditory characteristic, or a new set of adjustment parameters, may be provided to the hearing aid by a host programming device which includes a mechanism for communicating with the hearing aid being programmed.
Such programmable hearing aids may be programmed specifically to provide an auditory characteristic which, it is hoped, will compensate for the measured hearing impairment of the user. However, while the programming of such hearing aids may be digital, and thus very precise, the actual signal processing circuitry of the hearing aid may very well be analog. Because there are variations between individual analog components, at least in part due to semiconductor process variation, the actual auditory characteristic provided by a given individual hearing aid may be somewhat different than that actually "prescribed" by the programming system. Further, other characteristics of the individual hearing aid, such as model number, revision number, manufacturing date code, serial number and optional features actually contained in the hearing aid, may be important to the programming system of the hearing aid and need to be manually input by the programming system into the fitting process. Such manual input is not only inconvenient but also is a source of error which could cause a less than optimum fitting to be obtained.
U.S. Pat. No. 4,548,082, Engebretson et al, Hearing Aids, Signal Processing Systems For Compensating Hearing Deficiencies, and Methods, discloses the use of "calibration" information, which may be stored in the memory of the hearing aid, in the programming of a digital hearing aid (column 16, lines 13-22). The "calibration" information contemplated by Engebretson et al are transfer functions (column 24, line 57 through column 25, line 6) which provide a factory estimate of the hearing aid/probe microphone/ear canal interface referred in the context of "ear volume" (column 14, line 28 through column 16, line 12). In order to make this data usable it must be adjusted to take into account the actual hearing aid/patient interface data instead of the factory data using the "standard coupler" (column 16, lines 23-36). Engebretson et al stores a sufficient transfer function, i.e., a sufficient set of the acoustic relationship from the input to the output of the hearing aid, taken at four different frequencies. Since the sufficient transfer function data encompasses a large volume of data, data for only four distinct frequencies can be stored. The acoustic relationship of input and output must then be interpolated from this data.